1. Field of the Invention
The present invention relates to a method and apparatus for encoding the position of a component.
2. Description of the Related Art
Frequently when a controller electrically controls the position of a mechanical component, it is desirable to have feedback indicating the position of the mechanical component. Such feedback provides the controller with an indication of the present position of the mechanical component being controlled. One application for such position feedback is in a transfer case motor for a four-wheel-drive vehicle. Such a motor drives a component, typically a cam, typically in a rotary motion. The motion of the cam facilitates shifting of the transfer case into various gear states such as "two-wheel-drive high", "four-wheel-drive low", "four-wheel-drive high", and "neutral".
A typical way of encoding the position of a mechanical component is with a "contact plate". Such a contact plate is coupled to the mechanical component whose position is being controlled. As the component moves, the contact plate moves as well. The contact plate typically has a number of electrically conductive areas disposed such that the contact plate produces a binary code which represents the position of the mechanical component. The binary code is sent from the contact plate via a series of conductive brushes positioned in contact with the contact plate. Each brush is typically connected to electronic circuitry designed to read the signal on the brush. The signal on each brush represents a binary digit (a "bit"). The bits represented by the signals on the brushes form the binary codes which indicate the position of the mechanical component being controlled.
It is desirable for a position encoding scheme to have a number of features. First, when the mechanical component being controlled travels from one "particularly significant" position to another, a single one of the circuits can be monitored for indication that the mechanical component has reached its destination position. That allows simplified detecting of the movement of the mechanical component, as only one circuit needs to be monitored by the device which is reading the signals from the contact plate. "Particularly significant" positions of a typical transfer case motor are the gear states mentioned above. Other positions of a transfer case motor typically encoded by a contact plate are intermediate positions between those gear states.
A second desirable feature of an encoding scheme is that the switching of that single circuit just mentioned always be in the same direction (that is, low voltage to high voltage or high voltage to low voltage). That helps to simplify the device which is reading the signals generated by the encoding scheme.